All About Computer Viruses

by: Kara Glover


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Date of copyright: November 2004

All About Computer Viruses
by Kara Glover
kara333@earthlink.net

Your computer is as slow as molasses. Your mouse freezes every 15 minutes, and that Microsoft Word
program just won’t seem to open.

You might have a virus.

Just what exactly is a virus? What kind is in your computer? How did it get there? How is it
spreading and wreaking such havoc? And why is it bothering with your computer anyway?

Viruses are pieces of programming code that make copies of themselves, or replicate, inside your
computer without asking your explicit written permission to do so. Forget getting your permission
down on paper. Viruses don’t bother to seek your permission at all! Very invasive.

In comparison, there are pieces of code that might replicate inside your computer, say something
your IT guy thinks you need. But the code spreads, perhaps throughout your office network, with
your consent (or at least your IT guy’s consent). These types of replicating code are called
agents, said Jimmy Kuo, a research fellow with McAfee AVERT, a research arm of anti-virus
software-maker McAfee Inc.

In this article, though, we’re not talking about the good guys, or the agents. We’ll be talking
about the bad guys, the viruses.

A long, long time ago in computer years, like five, most viruses were comprised of a similar
breed. They entered your computer perhaps through an email attachment or a floppy disk (remember
those?). Then they attached themselves to one of your files, say your Microsoft Word program.

When you opened your Microsoft Word program, the virus replicated and attached itself to other
files. These could be other random files on your hard drive, the files furthest away from your
Microsoft Word program, or other files, depending on how the virus writer wanted the virus to
behave.

This virus code could contain hundreds or thousands of instructions. When it replicates it inserts
those instructions, into the files it infects, said Carey Nachenberg, Chief Architect at Symantec
Research Labs, an arm of anti-virus software-maker Symantec. Corp.

Because so many other types of viruses exist now, the kind just described is called a classic
virus. Classic viruses still exist but they’re not quite as prevalent as they used to be. (Perhaps
we could put classic viruses on the shelf with Hemingway and Dickens.)

These days, in the modern era, viruses are known to spread through vulnerabilities in web
browsers, files shared over the internet, emails themselves, and computer networks.

As far as web browsers are concerned, Microsoft’s Internet Explorer takes most of the heat for
spreading viruses because it’s used by more people for web surfing than any other browser.

Nevertheless, “Any web browser potentially has vulnerabilities,” Nachenberg said.

For instance, let’s say you go to a website in IE you have every reason to think is safe,
Nachenberg said.

But unfortunately it isn’t. It has virus code hidden in its background that IE isn’t protecting
you from. While you’re looking at the site, the virus is downloaded onto your computer, he said.
That’s one way of catching a nasty virus.

During the past two years, another prevalent way to catch a virus has been through downloads
computer users share with one another, mostly on music sharing sites, Kuo said. On Limewire or
Kazaa, for instance, teenagers or other music enthusiasts might think they’re downloading that
latest Justin Timberlake song, when in reality they’re downloading a virus straight into their
computer. It’s easy for a virus writer to put a download with a virus on one of these sites
because everyone’s sharing with everyone else anyway.

Here’s one you might not have thought of. If you use Outlook or Outlook Express to send and
receive email, do you have a preview pane below your list of emails that shows the contents of the
email you have highlighted? If so, you may be putting yourself at risk.

Some viruses, though a small percentage according to Nachenberg, are inserted straight into emails
themselves.

Forget opening the attachment. All you have to do is view the email to potentially get a virus,
Kuo added. For instance, have you ever opened or viewed an email that states it’s “loading”? Well,
once everything is “loaded,” a virus in the email might just load onto your computer.

So if I were you, I’d click on View on the toolbar in your Outlook or Outlook Express and close
the preview pane. (You have to click on View and then Layout in Outlook Express.)

On a network at work? You could get a virus that way. Worms are viruses that come into your
computer via networks, Kuo said. They travel from machine to machine and, unlike, the classic
viruses, they attack the machine itself rather than individual files.

Worms sit in your working memory, or RAM, Nachenberg said.

OK, so we’ve talked about how the viruses get into a computer. How do they cause so much damage
once they’re there?

Let’s say you’ve caught a classic virus, one that replicates and attacks various files on your
computer. Let’s go back to the example of the virus that initially infects your Microsoft Word
program.

Well, it might eventually cause that program to crash, Nachenberg said. It also might cause damage
to your computer as it looks for new targets to infect.
This process of infecting targets and looking for new ones could eventually use up your computer’s
ability to function, he said.

Often the destruction a virus causes is pegged to a certain event or date and time, called a
trigger. For instance, a virus could be programmed to lay dormant until January 28. When that date
rolls around, though, it may be programmed to do something as innocuous but annoying as splash
popups on your screen, or something as severe as reformat your computer’s hard drive, Nachenberg
said.

There are other potential reasons, though, for a virus to cause your computer to be acting slow or
in weird ways. And that leads us to a new segment – the reason virus writers would want to waste
their time creating viruses in the first place.

The majority of viruses are still written by teenagers looking for some notoriety, Nachenberg
said. But a growing segment of the virus-writing population has other intentions in mind.

For these other intentions, we first need to explain the “backdoor” concept.

The sole purpose of some viruses is to create a vulnerability in your computer. Once it creates
this hole of sorts, or backdoor, it signals home to mama or dada virus writer (kind of like in
E.T.). Once the virus writer receives the signal, they can use and abuse your computer to their
own likings.

Trojans are sometimes used to open backdoors. In fact that is usually their sole purpose, Kuo
said.

Trojans are pieces of code you might download onto your computer, say, from a newsgroup. As in the
Trojan War they are named after, they are usually disguised as innocuous pieces of code. But
Trojans aren’t considered viruses because they don’t replicate.

Now back to the real viruses. Let’s say we have Joe Shmo virus writer. He sends out a virus that
ends up infecting a thousand machines. But he doesn’t want the feds on his case. So he instructs
the viruses on the various machines to send their signals, not of course to his computer, but to a
place that can’t be traced. Hotmail email happens to be an example of one such place, Kuo said.

OK, so the virus writers now control these computers. What will they use them for?
One use is to send spam. Once that backdoor is open, they bounce spam off of those computers and
send it to other machines, Nachenberg said.

That’s right. Some spam you have in your email right now may have been originally sent to other
innocent computers before it came to yours so that it could remain in disguise. If the authorities
could track down the original senders of spam, they could crack down on spam itself. Spam senders
don’t want that.

Ever heard of phishing emails? Those are the ones that purport to be from your internet service
provider or bank. They typically request some information from you, like your credit card number.
The problem is, they’re NOT from your internet service provider or your bank. They’re from evil
people after your credit card number! Well, these emails are often sent the same way spam is sent,
by sending them via innocent computers.

Of course makers of anti-virus software use a variety of methods to combat the onslaught of
viruses. Norton, for instance, uses signature scanning, Nachenberg said.

Signature scanning is similar to the process of looking for DNA fingerprints, he said. Norton
examines programming code to find what viruses are made of. It adds those bad instructions it
finds to its large database of other bad code. Then it uses this vast database to seek out and
match the code in it with similar code in your computer. When it finds such virus code, it lets
you know!

©2004 by Kara Glover














About the author:
Kara Glover is a Computer Tutor and Troubleshooter.
You can find her articles and tutorials on topics such as
Microsoft Word®, Excel®, and PowerPoint® on her website: http://www.karathecomputertutor.com



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